Mn$_3$O$_4$(001) film growth on Ag(001) - a systematic study using NEXAFS, STM, and LEED

TL;DR

This study systematically investigates the growth and structural evolution of Mn₃O₄(001) films on Ag(001) using NEXAFS, STM, and LEED, revealing phase transitions and surface restructuring during film development.

Contribution

It provides a detailed analysis of Mn₃O₄ film growth mechanisms and structural phase transitions on Ag(001), combining multiple surface characterization techniques.

Findings

Initial oxide islands exhibit p(2×1) and p(2×2) structures.

A phase transition occurs at higher thicknesses, introducing a c(2×2) structure.

Surface restructuring reduces surface energy in thicker films.

Abstract

The film growth of Mn$_3$O$_4$(001) films on Ag(001) up to film thicknesses of almost seven unit cells of Mn$_3$O$_4$ has been monitored using a complementary combination of near-edge X-ray absorption fine structure spectroscopy (NEXAFS), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED). The oxide films have been prepared by molecular beam epitaxy. Using NEXAFS, the identity of the Mn oxide has clearly been determined as Mn$_3$O$_4$. For the initial stages of growth, oxide islands with p(2$\times$1) and p(2$\times$2) structures are formed, which are embedded into the substrate. For Mn$_3$O$_4$ coverages up to 1.5 unit cells a p(2$\times$1) structure of the films is visible in STM and LEED. Further increase of the thickness leads to a phase transition of the oxide films resulting in an additional c(2$\times$2) structure with a 45$^\circ$ rotated atomic pattern. The emerging film structures are discussed on the basis of a sublayer model of the Mn$_3$O$_4$ spinel unit cell. While the polarity of the island edges determines the structure of initial islands, the surface energy of thicker layers is remarkably reduced by a film restructuring.